Android: App crashing when trying to load Data from API into a listview

Question

I'm trying to load a league table from an API into a listview, but the app keeps crashing when I access the activity with the league table, any thoughts ?

FootballAysncTask.Java

package gatt.geordey.homeassignment;

import android.os.AsyncTask;

import org.json.JSONException;

/**
 * Created by Geordey on 07/04/2017.
 */

public class FootballAsyncTask extends AsyncTask<String, Void, String> {

    @Override
    protected String doInBackground(String... params){

        String data = ((new FootballHttpClient()).getStandings());

        String result = "";
        try {
            result =JSONFootballParser.getTeamName(data);
        }catch (JSONException e) {
            e.printStackTrace();
        }

        return result;
    }
}

FootballHttplient.Java

package gatt.geordey.homeassignment;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

/**
 * Created by Geordey on 07/04/2017.
 */

public class FootballHttpClient {

    private static String BASE_URL = "http://api.football-data.org/v1/";

    public String getStandings(){
        HttpURLConnection con = null;
        InputStream is = null;

        try {
            String url = BASE_URL + "competitions/438/leagueTable";

            con = (HttpURLConnection) ( new URL(url)).openConnection();
            con.setRequestMethod("GET");
            con.setDoInput(true);
            con.setDoOutput(true);
            con.connect();

            //read the response
            StringBuffer buffer = new StringBuffer();
            is = con.getInputStream();
            BufferedReader br = new BufferedReader(new InputStreamReader(is));
            String line = null;
            while (  (line = br.readLine()) != null )
                buffer.append(line + "\r\n");

            is.close();
            con.disconnect();

            return buffer.toString();
        }
        catch(Throwable t) {
            t.printStackTrace();
        }
        finally {
            try { is.close(); } catch(Throwable t) {}
            try { con.disconnect(); } catch(Throwable t) {}
        }

        return null;
    }
}

JsonFootballParser.Java

package gatt.geordey.homeassignment;

import org.json.JSONException;
import org.json.JSONObject;

/**
 * Created by Geordey on 07/04/2017.
 */

public class JSONFootballParser {

    public static String getTeamName(String data) throws JSONException{
        JSONObject jObj = new JSONObject(data);

        JSONObject mainObj = jObj.getJSONObject("standing");
        return mainObj.getString("teamName");
    }

}

Standings.Java

package gatt.geordey.homeassignment;

import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.view.ContextMenu;
import android.view.MenuInflater;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.concurrent.ExecutionException;

public class Standings extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_standings);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.setDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);

        TextView test = (TextView) findViewById(R.id.test);
        ListView standings = (ListView) findViewById(R.id.standings);

        ArrayAdapter<String> listAdapter;
        ArrayList teamNames = null;

        FootballAsyncTask task = new FootballAsyncTask();
        try{
            String teamName = task.execute().get();
            teamNames.add(teamName);

        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }

        listAdapter = new ArrayAdapter<String>(this, R.layout.row, teamNames);
        standings.setAdapter(listAdapter);
    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.teams, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        if (id == R.id.nav_teams) {
            // Handle the team intent
            Intent showTeams = new Intent(this,Teams.class);
            startActivity(showTeams);

        } else if (id == R.id.nav_standings) {
            // Handle the Standings intent
            Intent showStandings = new Intent(this,Standings.class);
            startActivity(showStandings);

        } else if (id == R.id.nav_fixtures) {
            // Handle the Fixtures intent
            Intent showFixtures = new Intent(this, Fixtures.class);
            startActivity(showFixtures);

        } else if (id == R.id.nav_favourites) {
            // Handle the Favourites intent
            Intent showFavourites = new Intent(this, Favourites.class);
            startActivity(showFavourites);

        } else if (id == R.id.nav_logout){
            // Handle the Logout intent
            // End Session

        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }
}

Error Image

Answer 1

i think task.execute().get(); returning null

just try with only task.execute(); And try to use recyclerview

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
     .....
    }

when you use listvew and filling with data that time you need getview method

Answer 2

You are never initializing the teamNames list.

ArrayList teamNames = null;

...

teamNames.add(teamName);

The array adapter is instantiated with the null list, and crashes when is set to the listview.

The reason why the code gets until that point is because you are catching exceptions. You can see the stacktrace on the screenshot printed in white.